DIAGNOSTIC ACCURACY AND FEATURE BASED ANALYSIS OF MRI FOR FISTULA-IN-ANO KEEPING SURGICAL FINDINGS AS GOLD STANDARD

Abstract

Background: Perianal fistulas are a frequent yet difficult anorectal disease needing thorough anatomical examination and customised surgical therapy. Preoperative surgical planning using magnetic resonance imaging (MRI) is becoming more common.  The objective of this study is to determine the diagnostic accuracy of magnetic resonance imaging for the diagnosis of anal fistula among clinically suspected patients, taking the surgical finding as gold standard. Material and Methods: This cross-sectional validation study was conducted from June 2025 to December 2025.We enrolled 264 male and female patients of age between 18-60 years presenting with clinically suspected fistula-in-ano, using non-probability consecutive sampling technique. MRI examination was performed using standardized technique and anal fistula on MRI was labelled as positive if there is T2 hyperintense appearance of the fistula tract, presence of hyperintense cavities, and rectal wall thickening. After that all patients underwent surgical treatment of anal fistula. Collected data was entered and analyzed on computer software SPSS version 25. Diagnostic accuracies were determined using a 2×2 table. Study confounders were controlled by the stratification. Agreement for various features of fistula-in-ano were also determined using kappa statistics. Results: Overall accuracy of MRI for detecting the fistula -in-ano was 88.6%; while, sensitivity, specificity, NPV and PPV were 90.6%, 82.0%, 72.5% and 94.4% respectively. Agreement analysis showed the highest agreement for horseshoe extension that was 71.2% and lowest for secondary tract that was 56.1%. However, corresponding k-values for all the features indicated poor agreement for all the features ranging from (-0.027 to 0.085). Conclusion: When compared to surgical results, MRI has superior diagnostic accuracy indices for identifying fistula in-ano in our local population. The performance of MRI was unaffected by any of the study confounders, which is a testament to its reliability and practicality in clinical settings. MRI should be regarded as an essential component of the diagnostic workup for the fistula-in-ano. Integration of the high-quality MRI with surgical expertise has the potential to improve the operative planning, reduce recurrence, and optimize patient outcomes.